Fitly PulseHow Much Water Should You Drink a Day?
There is no single number that fits everyone. How much fluid you need depends on your body size, how active you are, the climate you live in, and what you eat. This guide explains the commonly cited figures, the simple rule of thumb our calculator uses, and how to tell whether your own intake is about right.
What the official figures say
The U.S. National Academies of Sciences, Engineering, and Medicine sets an adequate intake for total water of about 3.7 litres per day for men and 2.7 litres per day for women (adults 19 and over). Two details matter:
- These figures cover total water from drinks and food. Roughly 20% usually comes from food such as fruit, vegetables, soup and rice.
- They are population-level averages for healthy people, not a target to force down. Many healthy people maintain good hydration on less.
What changes your water needs
- Body size. Larger bodies lose and use more water.
- Heat and humidity. In hot, humid climates you lose more through sweat, so needs rise noticeably.
- Exercise. Longer or harder sessions increase sweat losses.
- Illness. Fever, vomiting and diarrhoea increase fluid needs.
- Pregnancy and breastfeeding. Needs are higher; ask your doctor for personal guidance.
How our calculator estimates a target
The Fitly Pulse tracker uses a simple, transparent rule of thumb: about 35 ml per kilogram of body weight, plus an allowance that scales with your activity level. For a 70 kg adult with a moderate activity setting, that works out to roughly 2.9 litres of fluid per day.
This is a planning estimate, not a clinical prescription. Treat it as a starting point and adjust to how you feel, how hot it is, and what your doctor advises.
Are you drinking enough? Simple checks
- Urine colour. Pale straw-yellow generally suggests good hydration. Dark amber suggests you may need more fluid.
- Thirst. For most healthy adults, thirst is a reliable cue. Drink when thirsty, and more during heat or exercise.
- Frequency. Going many hours without urinating can be a sign of low intake.
Can you drink too much?
Yes, although it is uncommon. Drinking very large amounts in a short time can dilute blood sodium (hyponatraemia), which has been reported mainly in endurance events. Spread your fluids through the day rather than forcing large volumes at once. Some conditions, including certain heart, kidney and liver problems, require limiting fluids, so follow your doctor's advice if that applies to you.
Practical tips
- Drink a glass of water with each meal and when you wake up.
- Keep a bottle where you work and refill it on a schedule.
- Count other fluids too: tea, milk, soup and fruit all contribute.
- Increase intake on hot days and around exercise.
Try it yourself — the free Fitly Pulse tracker runs these calculations in your browser. No account needed.
Open the free trackerReferences
- National Academies of Sciences, Engineering, and Medicine (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. nap.nationalacademies.org/catalog/10925